Lean air

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Lean air is a gas mixture with an oxygen content lower than 20.95% (the oxygen content of the normal breathing air). Lean air is made from a gas mixture of air with nitrogen or of pure oxygen with nitrogen and is used in several production processes where a product covering with pure nitrogen can be dangerous, undesirable or more expensive. In some production processes the oxygen content is necessary for the reaction process or during storage (e.g. synthetic resin production, acrylic compounds such as acrylic acid (CAAC) or butyl acrylate (BA)).

Contents

Definition

Lean air is artificially produced "air" with a lower oxygen content. The normal oxygen content of 20.95 Vol .-% in air is reduced (leaned) to a lower proportion (e.g. 8 Vol.-%). For this purpose gases are mixed: Either compressed air with nitrogen or oxygen with nitrogen.

The generic term for Lean air is synthetic air which can refer to gas mixtures with a lower but also with a higher content of oxygen. Synthetic air is used e.g. used for gas analyzers as zero gas [1] [2] or operating gas for the detection of nitrogen oxides. In large scaled chemical processes the gas mixture is used in significantly larger quantities and there has an impact on product quality.

Usage

Lean air is often required in processes for the supply of solvent boilers and reactors, e.g. in the production of synthetic resins during Polymerization. In these processes, heat is added and combustible gases escape from the product. Three required factors of the combustion triangle (combustible substance, oxygen, ignition energy) would coincide spatially and temporally if produced under normal breathing air. This could lead to an explosion or deflagration, with consequent serious accidents.

If the product is acrylic acid, in opposite oxygen must be present and pure inert atmosphere must be avoided: "Overheating of Acrylic Acid must be avoided because this can lead to explosions." "Several case histories of Acrylic Acid were reported when procedures for proper handling or storage were disregarded." "Overlaying Acrylic Acid with a pure nitrogen atmosphere during the manufacturing process can lead to oxygen depletion" [3] and in consequence to explosion. Even storage leads to chemical reaction requiring oxygen. "Oxygen is consumed slowly during storage. Therefore the level of dissolved oxygen should be periodically replenished with air (or an oxygen/nitrogen gas mixture, 'lean air mixture')." [3] Thus the lean air, used for this purpose, has to be kept in a safe oxygen range so that accidents are prevented and at the same time that the reaction can take place.

Due to the regular use in potentially explosive areas, compliance with the oxygen content specified for the lean air, i.e. both for the quality of the production process (desired chemical reaction) and for safety-related matters (combustion triangle, overheating), is essential.

Lean air can be filled in gas cylinders (or bundles as storage banks) from manufacturers of technical gases [4] . When larger quantities are required, companies tend to operate their own systems for generating lean air because this is more cost effective. Systems for production of such gas mixtures are called gas mixers, or more specific lean air units. The demands of those lean air units for quantity, quality, security and availability are individually graded and are defined by company-specific needs and budgets.

Generation of lean air

Gas quality, safety and availability are important for the process [5] when generating lean air. That means in detail

Quality

As an additional measure to monitor the correct gas mixture quality, a gas analyzer can be used that continuously monitors the oxygen concentration. The measured oxygen value can be displayed and transferred to a higher-level process control system via an online connection. If the limit value is exceeded, a change in the quality of the gas mixture (in the case of automatic, dynamic lean air systems) can be initiated, and a shutdown or a switchover to a possibly existing bypass can be initiated.

Safety

The safe compliance with a defined oxygen concentration in the lean air influences the safety of the supplied process plant. Functional safety can be additionally increased by using a Safety Integrity Level analysis (SIL analysis). A SIL or security level is a security requirement level in accordance with the standard IEC 61508 / IEC 61511. The monitoring system used for this (usually consisting of a gas analyzer, shutdown, blow-off line solenoid valve) is assessed jointly with regard to its reliability by this SIL analysis. This further reduces the risk of potential malfunctions.

Availability

To ensure the availability of a professionally designed lean air system, at least the following measures are common: [6]

See also

Related Research Articles

Nitrox refers to any gas mixture composed of nitrogen and oxygen. This includes atmospheric air, which is approximately 78% nitrogen, 21% oxygen, and 1% other gases, primarily argon. In the usual application, underwater diving, nitrox is normally distinguished from air and handled differently. The most common use of nitrox mixtures containing oxygen in higher proportions than atmospheric air is in scuba diving, where the reduced partial pressure of nitrogen is advantageous in reducing nitrogen uptake in the body's tissues, thereby extending the practicable underwater dive time by reducing the decompression requirement, or reducing the risk of decompression sickness.

<span class="mw-page-title-main">Trimix (breathing gas)</span> Breathing gas consisting of oxygen, helium and nitrogen

Trimix is a breathing gas consisting of oxygen, helium and nitrogen and is used in deep commercial diving, during the deep phase of dives carried out using technical diving techniques, and in advanced recreational diving.

<span class="mw-page-title-main">Ammonium nitrate</span> Chemical compound with formula NH4NO3

Ammonium nitrate is a chemical compound with the formula NH4NO3. It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is predominantly used in agriculture as a high-nitrogen fertilizer.

An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to as the inert gases. Inert gases are used generally to avoid unwanted chemical reactions degrading a sample. These undesirable chemical reactions are often oxidation and hydrolysis reactions with the oxygen and moisture in air. The term inert gas is context-dependent because several of the noble gases can be made to react under certain conditions.

<span class="mw-page-title-main">Breathing gas</span> Gas used for human respiration

A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed habitats such as scuba equipment, surface supplied diving equipment, recompression chambers, high-altitude mountaineering, high-flying aircraft, submarines, space suits, spacecraft, medical life support and first aid equipment, and anaesthetic machines.

Cryogenic fuels are fuels that require storage at extremely low temperatures in order to maintain them in a liquid state. These fuels are used in machinery that operates in space where ordinary fuel cannot be used, due to the very low temperatures often encountered in space, and the absence of an environment that supports combustion. Cryogenic fuels most often constitute liquefied gases such as liquid hydrogen.

<span class="mw-page-title-main">Gas blending for scuba diving</span> Mixing and filling cylinders with breathing gases for use when scuba diving

Gas blending for scuba diving is the filling of diving cylinders with non-air breathing gases such as nitrox, trimix and heliox. Use of these gases is generally intended to improve overall safety of the planned dive, by reducing the risk of decompression sickness and/or nitrogen narcosis, and may improve ease of breathing.

An oxygen sensor (or lambda sensor, where lambda refers to air–fuel equivalence ratio, usually denoted by λ) or probe or sond, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analysed.

<span class="mw-page-title-main">Pressure swing adsorption</span> Method of gases separation using selective adsorption under pressure

Pressure swing adsorption (PSA) is a technique used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperature and significantly differs from the cryogenic distillation commonly used to separate gases. Selective adsorbent materials are used as trapping material, preferentially adsorbing the target gas species at high pressure. The process then swings to low pressure to desorb the adsorbed gas.

<span class="mw-page-title-main">Industrial gas</span> Gaseous materials produced for use in industry

Industrial gases are the gaseous materials that are manufactured for use in industry. The principal gases provided are nitrogen, oxygen, carbon dioxide, argon, hydrogen, helium and acetylene, although many other gases and mixtures are also available in gas cylinders. The industry producing these gases is also known as industrial gas, which is seen as also encompassing the supply of equipment and technology to produce and use the gases. Their production is a part of the wider chemical Industry.

<span class="mw-page-title-main">Oxy-fuel combustion process</span> Burning of fuel with pure oxygen

Oxy-fuel combustion is the process of burning a fuel using pure oxygen, or a mixture of oxygen and recirculated flue gas, instead of air. Since the nitrogen component of air is not heated, fuel consumption is reduced, and higher flame temperatures are possible. Historically, the primary use of oxy-fuel combustion has been in welding and cutting of metals, especially steel, since oxy-fuel allows for higher flame temperatures than can be achieved with an air-fuel flame. It has also received a lot of attention in recent decades as a potential carbon capture and storage technology.

Equivalent narcotic depth (END) (historically also equivalent nitrogen depth) is used in technical diving as a way of estimating the narcotic effect of a breathing gas mixture, such as nitrox, heliox or trimix. The method is used, for a given breathing gas mix and dive depth, to calculate the equivalent depth which would produce about the same narcotic effect when breathing air.

<span class="mw-page-title-main">Nitrogen generator</span>

Nitrogen generators and stations are stationary or mobile air-to-nitrogen production complexes.

<span class="mw-page-title-main">Cryogenic gas plant</span> Industrial facility that creates cryogenic liquid at relatively high purity

A cryogenic gas plant is an industrial facility that creates molecular oxygen, molecular nitrogen, argon, krypton, helium, and xenon at relatively high purity. As air is made up of nitrogen, the most common gas in the atmosphere, at 78%, with oxygen at 19%, and argon at 1%, with trace gasses making up the rest, cryogenic gas plants separate air inside a distillation column at cryogenic temperatures to produce high purity gasses such as argon, nitrogen, oxygen, and many more with 1 ppm or less impurities. The process is based on the general theory of the Hampson-Linde cycle of air separation, which was invented by Carl von Linde in 1895.

<span class="mw-page-title-main">Helium analyzer</span> Instrument to measure the concentration of helium in a gas mixture

A Helium analyzer is an instrument used to identify the presence and concentration of helium in a mixture of gases. In Technical diving where breathing gas mixtures known as Trimix comprising oxygen, helium and nitrogen are used, it is necessary to know the fraction of helium in the mixture to reliably calculate decompression schedules for dives using that mixture.

<span class="mw-page-title-main">Scuba gas planning</span> Estimation of breathing gas mixtures and quantities required for a planned dive profile

Scuba gas planning is the aspect of dive planning and of gas management which deals with the calculation or estimation of the amounts and mixtures of gases to be used for a planned dive. It may assume that the dive profile, including decompression, is known, but the process may be iterative, involving changes to the dive profile as a consequence of the gas requirement calculation, or changes to the gas mixtures chosen. Use of calculated reserves based on planned dive profile and estimated gas consumption rates rather than an arbitrary pressure is sometimes referred to as rock bottom gas management. The purpose of gas planning is to ensure that for all reasonably foreseeable contingencies, the divers of a team have sufficient breathing gas to safely return to a place where more breathing gas is available. In almost all cases this will be the surface.

<span class="mw-page-title-main">Scuba gas management</span> Logistical aspects of scuba breathing gas

Scuba gas management is the aspect of scuba diving which includes the gas planning, blending, filling, analysing, marking, storage, and transportation of gas cylinders for a dive, the monitoring and switching of breathing gases during a dive, efficient and correct use of the gas, and the provision of emergency gas to another member of the dive team. The primary aim is to ensure that everyone has enough to breathe of a gas suitable for the current depth at all times, and is aware of the gas mixture in use and its effect on decompression obligations, nitrogen narcosis, and oxygen toxicity risk. Some of these functions may be delegated to others, such as the filling of cylinders, or transportation to the dive site, but others are the direct responsibility of the diver using the gas.

Gas blending is the process of mixing gases for a specific purpose where the composition of the resulting mixture is specified and controlled. A wide range of applications include scientific and industrial processes, food production and storage and breathing gases.

Diving support equipment is the equipment used to facilitate a diving operation. It is either not taken into the water during the dive, such as the gas panel and compressor, or is not integral to the actual diving, being there to make the dive easier or safer, such as a surface decompression chamber. Some equipment, like a diving stage, is not easily categorised as diving or support equipment, and may be considered as either.

<span class="mw-page-title-main">Diving rebreather</span> Closed or semi-closed circuit scuba

A Diving rebreather is an underwater breathing apparatus that absorbs the carbon dioxide of a diver's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is added to replenish the amount metabolised by the diver. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment. The purpose is to extend the breathing endurance of a limited gas supply, and, for covert military use by frogmen or observation of underwater life, to eliminate the bubbles produced by an open circuit system. A diving rebreather is generally understood to be a portable unit carried by the user, and is therefore a type of self-contained underwater breathing apparatus (scuba). A semi-closed rebreather carried by the diver may also be known as a gas extender. The same technology on a submersible or surface installation is more likely to be referred to as a life-support system.

References

  1. ↑ "Synthetic Air" . Retrieved 2020-02-19.
  2. ↑ "Air -Delivering a wide range of synthetic and compressed air cylinder options to meet your varied needs" . Retrieved 2020-02-19.
  3. 1 2 EBAM – European Basic Acrylic Monomer Group. "Safe Handling And Storage of Acrylic Acid" (PDF). Brochure. European Basic Acrylic Monomer Manufacturers Association (EBAM) which is a Sector Group of the European Chemical Industry Council (Cefic). Third edition: 83.
  4. ↑ "Synthetic Air – Ellenbarrie industrial Gases" . Retrieved 2020-08-27.
  5. ↑ Hanf, Alexander (2017-01-15). "Lean Air Units" (PDF). Retrieved 2020-02-19.
  6. ↑ Hanf, Alexander. "Lean Air Units" (PDF). Retrieved 2020-02-19.
  7. ↑ "Safe lean-air supply for resin processes". www.coatings-group.com/. Retrieved 2021-07-06.
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